Intelligent restraining systems or airbag systems for motor vehicles using various sensors to determine whether a vehicle occupant is located directly in the space where the airbag is deployed have been under development for some time. When the airbag is deployed the quantity of gas flowing into the airbag will be reduced as much as possible, in order to avoid any injuries owing to the airbag. To date, multistage gas generators have been used predominantly to set the quantity of the gas flowing into the airbag. In these multistage gas generators, the total quantity of gas generant is subdivided into a plurality of units that are ignited either all at the same time or with a time offset, or of which only individual units are ignited. In the case of so-called hybrid gas generators, the ignition of only one stage ensures that the entire compressed gas already flows into the airbag. The ignition of a second, or further stages then leads only to a rise in temperature and thus a rise in pressure of the gas, but increases the volume of gas only insignificantly. However, the mass of gas exerts a substantial influence on the energy of the unfolding airbag, and is therefore also attended by a possible risk of injury to a vehicle occupant from the airbag.
The two-stage gas generators used to date are of very complicated construction, with the result that these gas generators also entail increased production costs. Furthermore, particularly in the case of the hybrid gas generators, it is difficult to reduce the volume of the gas flowing into the airbag, should this be desired.
Also known are airbag modules in which gas distribution devices are arranged on the gas generator. These gas distribution devices provide outflow openings that are sealed by means of flaps. These flaps can be opened if appropriate, with the result that some of the gas flows off not into the airbag, but into the environment through the outflow openings. The volume of the gas flowing into the airbag can therefore be reduced. However, such a gas distribution device permits only indirect, and thus imprecise, setting of the volume of gas flowing into the airbag. The mass of gas flowing into the airbag can be reduced by this device only to a specific value, a further reduction beyond this value being impossible.
It is the object of the invention to create an improved airbag module that has a gas distributor and permits a more precise setting of the mass of gas entering the airbag.
The object is achieved by means of an airbag module with a gas distributor that is arranged between a gas generator and an airbag.
In the airbag module according to the invention, a gas distributor is arranged between a gas generator and an airbag. The gas distributor has at least a first and a second flow path for a gas. At least one valve device for opening or closing the respective flow path is arranged in each case in the flow paths. In this case, the first flow path connects the gas generator to the airbag, while the second flow path is not connected to the airbag. Because of this arrangement, it is possible, by appropriately driving or setting the valve devices, for the gas generated by the gas generator to be introduced specifically into the airbag through the first flow path, or to be led off from the airbag through the second flow path. It is possible for a superfluous quantity of gas which is not required to fill the airbag or, because of a specific position of a vehicle occupant, is not desired to be led off via the second flow path so that it does not flow into the airbag. It is also possible to reduce the cross section of the first flow path by means of a valve device located therein, and thus to reduce the quantity and/or mass of the gas flowing into the airbag. When the valve device in the first flow path is completely closed, it is possible virtually entirely to prevent gas flowing into the airbag. Depending on the configuration of the valve device, it is then only a residual quantity of gas that flows into the airbag. As a rule, this residual quantity cannot be avoided, since no sealing means which could seal completely are provided on the valve devices used here. However, such a residual quantity of gas, for example 20% of the normal quantity which flows into the airbag, is insignificant, since it cannot fill the airbag to such an extent that the latter can pose a risk of injury to a vehicle occupant.
The second flow path advantageously connects the gas generator to at least one outflow opening. This outflow opening is advantageously arranged such that the outflowing gas flows away from the vehicle occupant. In the case of a driver's or passenger's airbag, such an outflow opening is therefore preferably positioned such that the gas flowing out through it is led off into the instrument panel of the motor vehicle. Thus, a superfluous quantity of gas, which is not required in a specific case to fill the airbag because the latter is not to be completely filled owing to a specific position of the vehicle occupant to be protected, can be safely disposed of without the risk of injury to the vehicle occupant from hot gas which is led off into the environment.
The valve devices are preferably coupled in such a way that the total flow cross section of the flow paths remains constant in each position of the valve devices. It can be ensured in this way that when one of the valve devices is being closed the total flow cross section through which the gas generated by the gas generator can flow off is not reduced to such an extent as to cause an impermissible increase in the gas pressure in the gas generator or the gas distributor. Given appropriate coupling of the valve devices, it can be ensured that when one valve device reduces the cross section of a flow path, the other valve device simultaneously enlarges the cross section of the other flow path by the same amount so that the total flow cross section remains essentially constant, and actuating the valve devices cannot lead to an increase in the internal pressure in the gas generator and in the gas distributor.
It is preferred to provide at least one explosive propellant charge for actuating the valve devices. Such a propellant charge comprises, for example, a detonating pill that, like the gas generator as well, can be ignited electrically by an appropriate control device. The propellant charge then abruptly generates a specific quantity of gas that, for example, can drive in the valve device a piston that actuates the latter to change the flow cross section in the appropriate flow path. The actuation of the valve devices by propellant charges has the advantage of permitting an exceptionally rapid actuation of the valve devices such as is required in the case of an airbag module whose airbag is deployed in a few milliseconds. In a way that is also preferred, the propellant charges actuate the valve devices in such a way that the latter virtually completely seal or completely open the appropriate flow path. Absolutely tight sealing of the flow paths is mostly not necessary, and so it is possible to do without expensive seals.
It is expedient to provide locking means for locking the valve devices in predetermined valve positions. These locking means permit the valve devices to be fixed in their end positions so that they cannot move back unintentionally, for example because of vibrations which are acting on the airbag module, something which could lead to re-release or resealing of the corresponding flow path, and thus to malfunctioning of the airbag module. The locking means are preferably constructed in the form of latching or clamping means which reliably retain the valve devices in the appropriate positions.
The valve devices of the first and the second flow paths advantageously have at least one common, movable slide, it being the case that the first flow path is open and the second flow path is closed in a first position of the slide, and the first flow path is closed and the second flow path is open in a second position of the slide. When the vehicle occupant is located too close to the airbag module, this embodiment renders it possible for the airbag to be inflated only slightly or virtually not at all by virtue of the fact that the first flow path, which connects the gas generator to the airbag, is closed. The fact that a common slide simultaneously opens the second flow path correspondingly renders it possible to ensure that the quantity of gas not required to fill the airbag is reliably directed through the second flow path, with the result that no undesired or impermissible overpressure can be produced in the gas generator or the gas distributor.
It is preferred for a propellant charge to be arranged in such a way that the slide can be moved from its first into its second position by igniting the propellant charge. When the propellant charge is ignited, a pressure is abruptly produced which abruptly moves the slide from its first position into the second. An extremely fast movement of the slide is thereby possible, with the result that the quantity of gas flowing into the airbag before the closure of the first flow path can be kept low.
The slide is preferably guided in a sliding fashion in a guiding device. In this way, a reliable and specific movement of the slide is rendered possible without jamming or tilting, with the result that malfunctioning of the valve devices can be prevented.
It is also preferred for the guiding device to have locking means for locking the slide in the region of the second position of the slide. The locking means retain the slide in the second position, in which the first flow path is closed, so that it cannot move back and inadvertently clear the first flow path again, something which would lead to undesired further filling of the airbag.
In a further embodiment, two first and two second flow passages and two slides are arranged, it being possible for the two slides to be moved, preferably independently of one another, in order in each case to close a first flow path and simultaneously to open a second flow path. This means that there are two flow paths connecting the gas generator to the airbag. Furthermore, corresponding to each of said first flow paths is a corresponding second flow path which, if appropriate, serves to direct a quantity of gas not required to inflate the airbag. Preferably, the two flow paths connecting the gas generator to the airbag can be sealed independently of one another by a separate slide in each case. This results in further possibilities for setting and/or controlling when filling the airbag. For example, the two first flow paths can be open so that the airbag is filled completely, but it is also possible for one or both of the first flow paths to be sealed so that the airbag is inflated only partially or virtually not at all. It is also preferred that in this case the two first flow paths can have different cross sections so that, depending on which of the two flow passages is sealed by a slide, it is possible to set a different inflation pressure strength for the airbag. At the same time, however, each slide opens the associated second flow path, thus ensuring that the quantity of gas which does not flow into the airbag through a first flow path is led off reliably through a corresponding second flow path. It is expedient for this purpose for the second flow path to have the same cross section as the first flow path to ensure that the quantity or volume of gas not required is directed completely away from the airbag and there is no impermissible increase in the internal pressure of the gas distributor or of the gas generator. The invention is not limited to the number of flow paths described here, rather it is also possible to arrange more flow paths, the flow paths advantageously being configured such that upon actuation of the valve devices the total flow cross section always remains essentially constant.
The slide is preferably arcuate and guided in an annular channel that is arranged concentrically with a gas outlet device of a gas generator. An exceptionally compact configuration of the gas distributor can be achieved in this way. Thus, the gas distributor can be arranged around a gas outlet device of a known gas generator without the need for additional modifications to the gas generator.
The flow paths are preferably constructed as openings that extend transverse to the direction of movement of the slide through the annular channel. The slide can thus move in the annular channel transverse to a flow direction of the gas flowing through the openings, and seal or clear the corresponding openings.
A detonator housing is connected to the annular channel for holding a propellant charge and is arranged on the annular channel behind the slide in the direction of movement. In this way, an appropriate propellant charge for moving the slide can be arranged directly on the annular channel, with the result that a shockwave produced upon ignition of the propellant charge enters the annular channel directly and accelerates or moves like a piston the slide guided there.
The second flow path can connect the gas generator to a further airbag. In this arrangement, the gas distributor can be used to inflate different airbags by one and the same gas generator, for example depending on the position of a vehicle occupant. The gas distributor switches over between appropriate flow paths that connect the gas generator to different airbags.